Title

In the event a secure Session Initiation Protocol (SIP) connection fails, the connection must be restricted from resorting to the unencrypted HTTP. (Cat II impact)

Discussion

Lync 2013 provides a single, unified client for real-time communications, including voice and video calls, Lync Meetings, presence, instant messaging, and persistent chat. The Lync client has a fall back option so that, in the event the Lync client cannot make a secure SIP connection to the Lync server, it will fall back to an unencrypted HTTP connection. In that event, all traffic will be unencrypted and in clear text. The configuration must be set to prevent HTTP being used for SIP connections in the event TLS or TCP fail.

Check Content

Verify the policy value for Computer Configuration -> Administrative Templates -> Microsoft Lync 2013 -> Microsoft Lync Feature Policies "Disable HTTP fallback for SIP connection" is set to "Enabled". Procedure: Use the Windows Registry Editor to navigate to the following key: HKLM\Software\Policies\Microsoft\office\15.0\lync Criteria: If the value disablehttpconnect is REG_DWORD = 1, this is not a finding.

Fix Text

Set the policy value for Computer Configuration -> Administrative Templates -> Microsoft Lync 2013 -> Microsoft Lync Feature Policies "Disable HTTP fallback for SIP connection" to "Enabled".

Additional Identifiers

Rule ID: SV-52836r2_rule

Vulnerability ID: V-40778

Group Title: DTOO422 - Session Initiation Protocol (SIP)

Expert Comments

CCIs tied to check.

Controls tied to check. These are derived from the CCIs shown above.